Difference between imperfeito, pretérito perfeito, and pretérito perfeito/imperfeito do indicativo?

Question

What is the different meanings of the past verb tenses in (Brazilian) Portuguese? I understand the general idea that the perfect preterite describes an action that completed in the past and the imperfect preterite describes a habitual or ongoing action, but I am really confused about the difference between something like 'estava chovendo' and 'chovia.'

Both seem to describe an ongoing action in the past, but I have a vague feeling that the first is like a one-time occurrence and the second describes something that tended to occur pretty often. Is there a correspondence to past forms in French, like 'j'avais eu' (I had had previously), 'j'avais' (I had), and 'j'ai eu' (I had had)?

For example:

Perfect preterite: choveu (it rained) describes a complete action that occurred in the past.

Imperfect preterite: chovia (it was raining)

Indicative perfect preterite: estava chovendo (it was raining)

Indicative imperfect preterite: choveu, same as standard imperfect preterite?

Here's another example: vinham/vieram/estavam vindo.

I am not sure the above labels are even correct, that is just my understanding from a grammatical book I have been trying to use.

Answer 1

Your feeling is pretty much correct. Estava chovendo refers to a particular occasion or a particular point in time, such as the moment I left home:

Quando eu saí de casa, estava chovendo muito [when I left home, it was raininig a lot]

You could in this example say “chovia muito”, but you’re more likely to find that in literature than in colloquial speech. But if you mean something that used to happen ― not just at one particular point in time ― then you use chovia:

Quando eu era criança, chovia mais do que agora [when I was a child it used to rain more than nowadays]

It’s the same with estavam vindo, vinham

Eles estavam vindo para casa quando eu os encontrei [they were coming home when I met them]

Eles vinham cá muitas vezes [They used to come here often]

More examples:

Eu estava lendo, e então faltou a luz [I was reading, and then the lights went out]
Dantes eu lia o jornal todos os dias [I used to read the newspaper every day]

Eu estava correndo, tropecei e caí [I was running, tripped and fell]
Quando eu era mais novo, corria 10 km in 30 minutes [When I was younger I would run 10 km in 30 minutes]

Eu estava gostando do livro, mas perdi o interesse no capítulo 10 [I was enjoying the book, but lost interest in chapter 10]
Em criança eu não gostava de couves [When I was child I wouldn’t like cabbage]

I’m pretty sure there will be lots of complications, but this is the gist of it.

Answer 2

The difference between estava + <verb in present participle> and <verb in imperfect indicative> depends on the verb in question and the context.

Estava + <verb in present participle>, just like in English, denotes the progressive aspect. For starters, this rules it out with non-phaseable states (like *ele estava a saber, *ele estava a ser alto), as it essentially turns the situations into states — but, yes, not into habitual states (which are actually derived from e.g. a series of events).

As to the imperfect indicative, a first observation is that in its normal usage (read: excepting here modal uses such as in conditional sentences or for courtesy), it needs some sort of temporal framing — this can be a temporal clause with quando/enquanto or some adverbial expression like muitas vezes, sempre, todos os meses (quantification) or ontem (temporal location, for states). The imperfect then indicates a intersection (partial or total) with some past, or a relationship of inclusion. Because of this, the imperfect may also alter the aspect of verb, eliminating its culmination and possibly even turning it into a state. For a state or an activity (like chover), which is atelic anyway (i.e., they don't tend to some completion), the effect is not as pronounced, but in something like:

Às 11h30, os mais retardatários ainda jantavam.

the culmination of jantar is lost and we can conclude they were dining before that time, and at the time of reference.

So the imperfect can, by itself, operate an aspect change close to estar + <present participle>, an indeed you could say estava jantando above. Likewise, quando cheguei a casa, chovia a potes and quando cheguei a casa, estava chovendo a potes are indistinguishable, though I agree with Jacinto that, in many cases, there is a small difference in register.

Only the imperfect, however, can describe habitual states:

Quando ligava a ventoinha, ela espirrava.
*Quando ligava a ventoinha, ela estava espirrando.

Espirrar, being a semelfactive, has no internal structure to focus, but the first sentence can instead be be read to mean every time I turned on the fan, she sneezed. This reading is not possible in the second sentence.

And in general, every time we use quantifiers such as sempre, todos os meses, com frequência, etc, estava + <verb in present participle> is not an option:

Antigamente, chovia durante o mês de Junho.
Ele jantava semanalmente em casa do amigo.